Compressor



G. NEIDL COMPRESSOR March 14, 1933.

. 3 Sheets-Sheet 1 Filed Oct. 8, 1951 March 14, 1933.

Fig.5 v

- Filed Oct. 1931 3 Sheets-Sheet 3 Patented Mar. 14, 1933 Warren STATES GEORG NEIDL, OF BERLIN, GERMANY CQMPBESSOR Application filed October 8, 1931, Serial No.

My invention relates toreciprocating. compressors or pumps whose inlet and delivery ports are controlled by the piston.

It is an object of my invention to so design a compressor or pump of this type that shocks in its driving mechanism are elimin-- ated and that, if designed as a compressor, the pump is particularly suitable for high speeds, as the stress on itsmechanism is reduced to a minimum, and its life is prolonged in proportion.

Tothis end I provide a member on the piston of the pump or compressor which isadapted to reciprocate in a separate chamher. This chamber is in permanent communication with the compression and expansion space of the cylinder through a passage whose free sectional area is small as compared with the piston surface.

In a preferred embodiment of my invention, I design the member as an axial extension or sleeve on the piston and provide the cylinder cover with an extension which projects into the cylinder and is spaced apart from its inner wall. In this manner the aforesaid chamber is formed at the outer end of the cylinder by an annular clearance between the wall of the cylinder and the extension of its cover. The passage by which permanent communication of the chamber and the compression and expansion space of the cylinder is effected, is obtained by making the inside diameter of the sleeve on the piston a little larger than the outside diameter of the extension.

In a machine designed on these lines, a cushion is always present in the chamber and the passage, with the exception of the inner' dead centre position of the piston in which the delivery port, or ports, is exposed by the piston, and of its outer dead centre position in which the inlet port, or ports, is exposed by the piston. In all other positions of its inward or compression stroke the piston is cushioned by the air or gas entrappedin the cylinder and in the chamber with which the cylinder is in permanent communication by the passage.

It is another object of my invention to vary the volume of the chamber which may be 567,631, and in Germany December 5, 1930.

effected by axially displacing the cylinder cover and its extension with respect to the cylinder.

Machines having pistons with a sleeve in combination with an inwardly projecting 5 part are old but in these machines the sleeve and the part serve as guiding means for the piston and there must be no clearance between the sleeve and the'part, as against my arrangement in which the sleeve acts as an annular plunger or cushioning member in the chamber and must not make a close fit with the inwardly projecting portion of the cylinder cover as this would interrupt the permanent communication between the cylinder and the chamber by the passage.

In the drawings aflixed to this specification and forming part thereof a compressor with a permanently fixed, and a compressor with an adjustable cylinder cover, both embodying my invention are illustrated diagrammatically by way of example.

In the drawings Fig. 1 is an axial section of the first compressor type.

Fig. 2 being an indicator diagram showing the operation of both compressor types,

Fig. 3 is an axial section of the second modification.

Referring to the drawings and first to Fig. '1', 1 is a cylinder 2 is a piston reciprocating within the cylinder. 3 is the gudgeon pin of the piston, 4: is an eccentric rod which is pivoted to the gudgeon pin 3 at its inner end, 6 is the driving shaft, and 5 is an eccentric on the driving shaft for operating the eccentric rod 4. 2 is a sleeve projecting from the inner face of the piston 2 and into an annular clearance or chamber 21 provided between the cylinder 1 and a projection 13 extending inwardly from the cylinder cover 13. 7 are two sets of piston rings on the sleeve 2' and 8 is one set of piston rings on the piston 2. 9 are ports in the wall of the sleeve 2 arranged to register in the inner dead centre position of the piston with delivery ports 10 and in its outer deadcentre position, with inlet or suction ports 11, provided in the wall of the cylinder 1. The ports 11 communicate with the atmosphere while the sleeve 2 and the outside diameter of the atmosphere.

extension 13. The length of the sleeve 2',.

the length of the extension 13 and the stroke of the piston 2, are so determined that the sleeve 2 never leaves the chamber 21.

The annular clearance or chamber 21, in addition to the elimination of shocks by the cushioningefiect explained above offers the advantage that in the manufacture and mounting of the compressor less fitting Work is required and that a large cooling surface is provided. The bottom of the extension 13 is formed with an opening 15 into which a valve (not shown) can be fitted to allow the machine to be started under no-load conditions.

While the compressor shown in Fig. 1 is single acting, it should be understood that my invention is not limited to single acting compressors but could be used as well in connection with double acting compressors.

The operation of this device is as follows:

As shown by the indicator diagram according to Fig. 2, s is the distance of the acting surface of the piston from the outer end wall of the extension 13. In its inner end position the acting surface of the piston attains its minimum distance s from the outer end wall of the extension 13. (Z is the diameter of the ports 10 and 11. 8 is the length of the cylinder wall between the ports 10 and 11. 8 is the difference between 8 and (1 The maximum stroke of the piston is equal to which corresponds to the position 4 shown at the bottom of Fig. 2, in which the ports 9 are in register with the ports 11 so that the interior R of the cylinder communicates with the When now the piston moves to the left into the position 3, the space R still communicates with the atmosphere so that the corresponding portion 1, 2 of the indicating curve is horizontal, coinciding with the line indicating the atmosphere pressure. When the piston is moved further to the left the ports 9 get out of register with the ports 11 and the space R is closed towards the atmosphere. During this movement the air in the space R is compressed according to the portion 2, 6 of the indicator diagram. Point 6 of the curve corresponds to position 2 of the piston in which the ports 9 register with the ports 10 so that the space R communicates with the air chamber (not shown) or the like. Assuming the output pressure to be 3 at mospheres, than the compressed air in the space R will expand from 8 atmospheres corresponding to point 6 to 3 atmospheres corresponding to point 4 of the indicator curve. Therefore the pressure will drop of a sudden from 6 to 4. If the piston moves to its inner end position (position 1) the air pressure remains constant and equal to the pressure in the air chamber or the like so that the corresponding portion 4, 5 of the indicator curve is horizontal, its distance from the abscissa axis gorresponding to the pressure in the air cham- On the return stroke of the piston the space R still communicates with the air chant ber until position 2 is reached, so that the corresponding portion of the indicator curve coincides with the portion 4, 5 except that it is passed in opposite direction. During the movement of the piston from position 2 to position 3 the space R is closed and the compressed air contained therein expands along the portion 4, 3 of the indicator curve. When position 3 is reached the space R is brought in communication with the atmosphere so that the indicator curve rises vertically from 3 to 2. During the movement of the piston from position 3 to position 4 the portion 1, 2 of the indicator curve is passed in opposite direction as before.

The indicator diagram is merely a theoretical one, the eflective diagram difi'ering somewhat in that the portions 2, 3 and 4, 6 are not exactly vertical etc.

If the clearance is made-too small the engine will knock heavily because in the portion 6, 4 at the indicator curve the air must escape too quickly through the ports 9, 10, being compressed in a too small clearance. If the clearanceis very small the point 6 of the indicator diagram has a very high position so that the portion 6, 4 is very. long and a large quantity of air must be discharged in a very short time. In consequence thereof the machine runs very hard so that the speed cannot be increased because the wear would be too great. On the other hand the engine may be run with a great number of revolutions since no valves are provided which could limit the speed by clattering orsticking. The clearance must be made larger as in the compressors hitherto known in order to render the engine operative at high speeds.

Owing to the increase of dimensions of the clearance the compression end pressure at the point 6 can be lowered without influencing the output pressure corresponding to point 4. It is true that by making the clearance larger the portion 2, 6 of the indicator diagram will be flattened so that the pressure 17 at the point 6 will drop, but the output pressure p is not decreased, for instance if the compressor feeds air to an air chamber in which a pressure p is maintained. By enlarging the clearance merely the hourly suction input is decreased provided that the clearance is not enlarged to such an extent that 9, becomes equal to or drops below 17 From the foregoing it will be seen that by varying the clearance the hourly suction input can be controlled without changing the output pressure..

- If it is required that no air should be delivered when a predetermined maximum pressure in an air chamber or the like is reached, the clearance must be so dimensioned that the pressure p is equal to the maximum pressure in the air chamber. The compressor will then force air into the air chamber Whenever the pressure in the chamber drops below its maximum value p until the maximum pressure is reached, the air feed being stopped and started automatically.

The clearance required for a given output pressure and a given suction input per hour can be computed as follows:

Be it assumed that during the pressure stroke of the piston from position 3 to'position 2 (corresponding to the portion 2, 6 of the indicator curve) Gr kg air are enclosed in the space R and Gro kg during the expanding stroke corresponding to the portion 4, 3

of the indicator curve. Then the weight of the air delivered from point 6 to point 4 is AG =G 709. v

Now according to the equation of condition lat '2 R-T and accordingly P3 a R-T the indices 2 and 3 corresponding to the points2 and 3 of the diagram. V and V are the corresponding volumes of the interior of the cylinder in cubicmetres.

Therefore V V 1 2 Pa' 3 M an 12-1".

The weight of the delivered air is equal to the Weight of the air sucked in so that Therefore the volume V sucked in per stroke is I p .V =AG .R.T

T is the absolute temperature of the air or the like. It is the gas constant. The pressures p are measured in icy/m From this follows Now V l cbm I from which follows 4 p3. cbm

Va vz'il l 1 2 3 From the diagram can be derived that In this equation f is the active piston surface measured 1n m If this formula is introduced into the equafrom which follows 1 V can be replaced by s From the equations 1 and 2 the following equations are derived if a polytropic expansion from point 6 to point 4 is assumed.

In these equations s is the distance indicating the clearance measured in metres. V is the hourly suction input of the compressor, the delivering degree, f the active piston surface measured in m 19 the initial pressure of the, compression, a the final pressure of the expansion, p. the initial pressure of the expansion, 72 the final pressure of the compression, all pressures being measured in leg/m m is the coehicient of the polytropic curve, 8 is the piston stroke and al is the axial length of the ports 9, both measured in m.

In the modification shown in Fig. 3 the with a flange 16, the cylinder jacket 12 with a corresponding flange 17, washers 18 being inserted between the flanges and the parts being held together by screw bolts 19 and nuts 20. By varying the number of washers 18 the distance :1: of the front wall of the cylinder cover 13 from the piston face in its inner dead centre position, can be varied.

The volume of chamber 21 might also be varied by other means (not shown), for instance by threading the cylinder and the cylinder cover and screwing the parts together so that by rotating the cylinder cover with respect to the cylinder the volume could be changed. In another embodiment (not shown) of my invention the cylinder 1 is axially adjustable with respect to the crank shaft 6 or the bearings of the crank shaftare adjustable with respect to the cylinder 1. It will be understood that by these means not only the volume of the chamber 1 but also the effective volume of the cylinder, and thereby the performance of the compressor is varied. It has already been suggested to provide adjustable means at the outer end of a cylinder for varying the effective volume of the cylinder but not to so design such means that a chamber is formed for a sleeve on the piston to reciprocate in.

Obviously my invention is not limited to compressors but might as well be applied to vacuum pumps.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to'a person skilled in the art.

In the claims afiixed to this specification no selection of any particular modification of the invention is intended to the exclusion of other modifications thereof and the right to subsequently make claim to any modification not coveredby these claims is expressly reserved.

I claim 1. In a reciprocating pump having a cylinder, a piston mounted to slide in said cylinder, and inlet and delivery ports ada ted to be controlled by said piston; a mem r on said piston adapted to move in a chamber which permanently communicates with the compression and expansion space of the cylinder through a passage whose free sectiona1 area is small as compared with the piston surface.

2 In a reciprocating pump having a cylinder, 9. piston mounted to slide in said cylinder, inlet and delivery ports adapted to be controlled by said piston, and a part projecting inwardly from the outer end of said cylinder and spaced apart from its inner Wall; a sleeve on said piston which is adapted to reciprocate in the chamber formed by the clearance between said part and the inner wall of said cylinder and whose inside diameter is larger than the outside diameter of said part, so that said part and said sleeve together form a passage through which the expansion and compression space of the cylinder permanently communicates with said chamber, the free sectional area of said passage being small as compared with the piston surface.

8. In a reciprocating pump having a cylinder, a piston mounted to slide in said cylinder, and inlet and delivery portsadapted to be controlled by said piston; a member on said piston adaptedzto move in a chamber which permanently communicates with the compression and expansion space of the cylinder through a passage whose free sectional area is small as compared with the piston surface, and means for varying the volume of said chamber.

In testimony whereof I aflix my signature.

GEORG NEIDL. 

